From TrenchlessTechnology.com (Jim Rush):
The Michigan Ditch is a 5.2-mile conveyance system that brings water from the high mountains into the Joe Wright Reservoir, a part of City’s two water sources. Over the years, the Michigan Ditch, a combination of pipeline and open channel originally built around 1900 and purchased by Fort Collins in the 1970s, was subject to the whims of Mother Nature. Specifically, one portion of the water supply route that crosses an area known as “the mudslide” was subject to periodic damage when the slides occurred.
The City was accustomed to making simple repairs that involved digging up the pipe and moving or replacing it when the slide moves. But in September 2014, crews noticed something unusual. The pipe, which typically moved only during snowmelt in the spring, had moved substantially since its repair that summer. The following spring, even more movement showed that a more permanent fix was needed.
“It was apparent that this wasn’t something we could simply dig up and put back in place like previous years,” said Owen Randall, chief engineer for Fort Collins Utilities. “We knew we needed a long-term solution that could cost upwards of $10 million. When I told City management the response was: ‘The water is worth $180 million, so go fix it.’”
In summer 2015, the City got to work with a geotechnical assessment that included seismic refraction as well as vertical and horizontal borings. Meanwhile, the City put together a team of consultants and contractors to help ascertain the best way to move forward. After exploring the options, the team decided that a tunnel that would re-route the water through the mountain in stable rock was the best solution…
The tunnel option provided the long-term solution the City was looking for while having the added benefits of less maintenance, less environmental impact and a construction cost comparable to other options…
The logistics of working on the side of a mountain also presented challenges. The project site was located 2.5 miles up a narrow, winding dirt road that dictated the weight and dimensions of the equipment that could be safely transported. Additionally, the nearest town (Walden, Colorado; population 3,000) was located 30 miles away, with Fort Collins 70 miles away. Even cell phone service had to be brought in.
“Due to the nature of the road, we were limited to about an 11-ft wide load,” said John Beckos, project manager for BT Construction. “We were unable to get a crane to the site, and the biggest excavators we could bring in were nearly hanging off the edge of the mountain on the way up.”
The site access also dictated the type of tunnel boring machine that could be used to excavate the tunnel. After evaluating the options, the project team elected to use an Akkerman hard-rock TBM that had a mixed face cutterhead to deal with the highly fractured, hard rock and abundant fault and shear zones. The machine was compact enough to accommodate the limited space at both the launch and retrieval pits, light enough to be handled by the available equipment, and had enough power to drill through rock that reached strengths of 15,000 psi…
The tunnel was mined from the downstream portal to the upstream portal. The first 40 ft of the alignment was straight before it transitioned into the 630-ft radius curve spanning 726 ft. The TBM was equipped with a conveyor system and dual muck boxes to remove the spoil. Spoil was stockpiled near the site to be used by the City for future repairs to the ditch and pipeline, as well as the access road, which the City also maintains…
Randall said the ground made tunneling a challenge. “The only thing consistent about the ground was that the rock was inconsistent,” he said. “We would find hard zones 2-3 inches thick, 2-3 feet thick and 30-feet thick. We knew we were going to get into difficult geology, but it still posed a challenge.”
Once the TBM was completely launched into the mountainside, the team had originally planned to be tunneling for about 6 weeks from early July through the middle of August. The inconsistent rock in the middle of the drive would end up slowing productions down and delaying the hole out until Sept. 29. And, despite the challenging ground, the TBM holed through precisely on target. Project team members credited the VMT guidance systems, typically used for larger and longer tunnels, for keeping the tunnel on line and grade…
Over the last 20 years, Fort Collins has implemented and refined its delivery system known as the Alternative Product Delivery System (APDS). Fort Collins retains a group of prequalified contractors and consultants on an annual contract basis – known as master service agreements – and when a project is needed, the City can call on its team of service providers with expertise in a particular area to negotiate a contract. This allows the City to quickly gather a team to develop the project from start to finish.
In the case of the Michigan Ditch Tunnel, the project team was brought on board to determine the best solution for the problem. As the project began to take shape as a tunnel, the City negotiated further contracts for tunnel design, construction and TBM procurement. The project team additionally developed a risk register to help identify and mitigate potential occurrences that could impact the project.
“Rather than trying to write a contract for the whole project up front, we can write contracts that are very well defined, knowing what our scope of work is going to be as planning and design progresses,” Randall said.
The added benefit of having the project team in place was that the project goals were defined by the team, rather than by an individual party or parties. “This was a very challenging and difficult project, but when you have everybody working toward the same goal, it makes all the difference in the world,” Randall added.
“The team functioned at a very high level and with great communication,” Dornfest said. “It was extremely challenging, but there was never any finger pointing and we were able to get the job done on schedule and under budget.”
Thanks to planning, teamwork and determination, the Michigan Ditch Tunnel project was successfully completed approximately $1 million below the initial budget of $8.5 million. The ditch system is now back online, assuring Fort Collins citizens of a reliable source of water for the years to come.
From The Fort Collins Coloradoan (Kevin Duggan):
The rotating cutting wheel of a custom-built tunnel boring machine began to slowly emerge from a mountainside around 5 a.m., said Owen Randall, chief engineer with Fort Collins Utilities.
The breakthrough was an exciting moment for crews that have been working on the 760-foot-long tunnel near Cameron Pass since June…
Crews still have four to six weeks of work to wrap up the project, which will carry Michigan Ditch and its valuable water to city-owned Joe Wright Reservoir.
Dismantling and removing a tunnel boring machine from the mountain will take three to four days. Hydraulic and electronic equipment used to operate the machine will be stripped from the tunnel before a 60-inch diameter pipe is installed to carry the water.
Weather could be a challenge as crews hustle to wrap up the project before heavy snowfall comes to the area. A few inches of snow fell last weekend, Randall said, but has since melted away…
Crews have been working on the project 24 hours a day since mid-September to make up for delays caused by equipment problems and the challenge of cutting through exceptionally hard rock.
Michigan Ditch provides the city with 2,000 to 3,000 acre-feet of raw water a year. The water is used to meet return flow obligations on the Poudre River mandated through various water-exchange agreements.
The market value of water supplied through the Michigan Ditch-Joe Wright Reservoir system is about $180 million, according to the city.
The tunnel project is in response to a slow-moving landslide that has been affecting the ditch for several years. Damage was especially severe in 2015.
City officials decided to protect the piped ditch by sending it through bedrock that the slide can’t affect. The project is expected to cost Fort Collins Utilities about $8.5 million.
For more information on the project, see http://fcgov.com/michigan-ditch-tunnel.
From the Fort Collins Coloradoan (Kevin Duggan):
After overcoming equipment problems and putting in 24-hour work days, crews on Wednesday were within 35 feet of reaching the end of what will be a 764-foot-long tunnel.
“We’ve made tremendous progress …,” said Owen Randall, chief engineer with Fort Collins Utilities. “We should be out sometime (Thursday) or Friday at the very latest.”
Breaking through the mountain will be done slowly and carefully to avoid destabilizing the mountainside, he said.
Crews still have four to six weeks of work to wrap up the project, which will carry Michigan Ditch and its valuable water to city-owned Joe Wright Reservoir near Cameron Pass.
Dismantling and removing a custom-built tunnel boring machine from the mountain will take three to four days. Hydraulic and electronic equipment used to operate the machine will be stripped from the tunnel before a 60-inch diameter pipe is installed to carry the water.
From The Fort Collins Coloradoan (Kevin Duggan):
A stretch of unusually hard rock inside a mountain near Cameron Pass has slowed a tunneling project aimed at shoring up Fort Collins’ water supply.
Progress on a 760-foot tunnel that will carry Michigan Ditch water to the city-owned Joe Wright Reservoir was stopped as of Thursday.
Crews are waiting for the arrival of replacement parts for the cutting head of a tunnel boring machine, or TBM, that was custom built for the project, said Owen Randall, chief engineer for Fort Collins Utilities.
Bearings on cutting disks on the rotating head have repeatedly burned out while dealing with a wall of pegmatite, a type of granite that can have various minerals and be exceptionally hard, Randall said.
Project managers are “literally looking around the world” for replacement disks, he said. When some will arrive at the work site is not known.
Rock conditions have varied tremendously during the course of the tunneling, which began in late June. Some layers of rock have been fractured and relatively easy to cut through, he said. Others have been difficult.
“We went 300 feet on the first set of disks,” Randall said. “We used up two sets going the next 8 feet. It’s just been very variable.”
Before the TBM was shut down, the cutting wheel was grinding out clouds of powder rather than chunks of rock, he said.
The machine was 482 feet into the mountain as of Thursday. Time and weather are becoming concerns as crews want to have the TBM off the mountain before heavy snow comes.
Randall said crews still expect to finish the project this fall.
Once the tunnel is cut, a 60-inch pipe made of fiberglasslike material will be put in place to carry Michigan Ditch. Randall said he wants to have water flowing through the pipe before the onset of winter.
“We are going to get through,” he said. “But safety will dictate how long we keep people working up here.”
Crews have been working seven days a week, 12 hours a day. That will increase to 24 hours a day Sept. 12. About 1,000 feet of pipe is expected to be delivered that week, Randall said.
The project is in response to a slow-moving landslide that has been affecting the ditch for several years. Damage was especially severe in 2015.